Adenosine triggers the nuclear translocation of protein kinase C epsilon in H9c2 cardiomyoblasts with the loss of phosphorylation at Ser729

Abstract

Adenosine is a major mediator of ischaemic preconditioning (IPC) and cardioprotection. The translocation and activation of protein kinase C epsilon, triggered by adenosine, are essential for these processes. We report here that H9c2 cardiomyoblasts express five PKC isoforms (alpha, beta(I), delta, epsilon and zeta). PKCepsilon is predominantly associated with F-actin fibres in unstimulated H9c2 cells but translocates to the nucleus on stimulation with adenosine. Cytosolic PKCepsilon associated with F-actin fibres is phosphorylated at Ser729 but nuclear PKCepsilon lacks phosphorylation at this site. Adenosine triggers the nuclear translocation after 5 min stimulation. PKCepsilon Ser729Ala and Ser729Glu mutants showed no translocation on adenosine stimulation suggesting both phosphorylation and serine at 729 are critical for this translocation. Among five PKC isoforms (alpha, beta(I), delta, epsilon and zeta) detected, PKCepsilon is the only isoform translocating to the nucleus upon adenosine stimulation. Disruption of microtubules (MTs), but not F-actin-rich fibres, blocked translocation of both endogenous PKCepsilon and overexpressed GFP-PKCepsilon to the nucleus. Ten proteins interacted with cytosolic PKCepsilon; five of which are components of myofibrils. Matrin 3 and vimentin interacted with nuclear PKCepsilon. These findings suggest that adenosine stimulates PKCepsilon translocation to the nucleus in H9c2 cells in a mechanism involving dephosphorylation at Ser729 and MT, which should advance our understanding of the signalling pathways stimulated by adenosine in IPC and cardioprotection.